Certain foodstuffs, such as fruits or products containing tomato, are usually packed in cans having an inner surface made at least in part of tin.
During thermal processing and also subsequent storage, the packed product takes up a certain amount of the tincoating, which preserves the organoleptic and visual properties of the product by minimising oxidation phenomenon.
To control the amount of tin available to the product packed therein, it is known to coat partially the inner tin surface of the cans with a suitable protective lacquer (also said protective varnish or coating).
Such partially lacquered cans are for example disclosed in documents EP-0 492 870 or EP-0 688 615.
In these documents, the can body is made from a tinplate, by drawing operation. The can obtained comprises a bottom element and a lateral wall which extends from the periphery of said bottom element; the upper border of said lateral wall defines an upper opening of the body intended to receive closing means.The can body comprises a unique lacquered surface, which extends continuously along a part of the height of the interior surface of its lateral wall; more precisely, said protective lacquered zone extends, in a continuous manner, from the upper border of the lateral wall and less than its length. The rest of the lateral wall (here its bottom) forms a unique exposed tin zone.
However, this type of current partially lacquered cans is not totally satisfying, since the inner surface of its side wall presents generally a blackened part which is particularly not aesthetic for the final consumer.
This blackened part corresponds to the exposed tin surface which contrasts with the lacquered zone of the lateral wall (which is generally particularly of light or clear colour); this blackening phenomenon is due to the chemical reaction with the conditioned foodstuff.